Frequency spectrum is valuable to operators of communication systems and therefore efforts continue to be made to increase usage of existing spectrum. At present each physical channel of a TDMA cellular communication system is allocated for use in any one cell by a single user or mobile station. It has been proposed to use a single physical channel for transmitting or receiving data intended for multiple mobile stations in a TDMA cellular communications system, thereby increasing usage of existing spectrum.
International patent application number PCT/US2009/031393, filed on 19 Jan. 2009, assigned to the assignee of this patent application, and incorporated herein by reference, describes using a single channel frequency and a single time slot (i.e. a single physical channel) for transmitting data two or more receiving apparatus. This application also describes using signalling training sequence set information to a remote station. For example, receiving signalling from a remote station indicating if a new set of training sequences is supported, and using a channel description to signal the training sequence set to be used by the remote station for a communication channel being established.
Using training-sequence-set-signal information uses communication bandwidth or capacity. It is therefore desirable to reduce bandwidth associated with signalling. It is particularly desirable to reduce signalling during a connection because bandwidth is more restricted during a connection than in a non-connected state. This applies especially to a circuit-switched or voice connection where minimal latency is allowable.
A mobile station with an advanced receiver can receive a signal containing two data streams intended for two mobile stations transmitted on a single physical channel and can decode both data streams. The mobile station can use interference cancellation to use one data stream as its own data and treat the other data stream as interference. Such an advanced receiver performs more processing and therefore consumes more battery current, when decoding more than one data stream, than a conventional receiver would consume when decoding a single data stream.
When at least one of the data streams is transmitted at half-rate using discontinuous transmission (DTX) and another data stream is transmitted at full rate, the signal will contain two data streams during some time intervals, and will contain only one data stream during other time intervals. A disadvantage is that the mobile station with the advanced receiver may perform more processing and consume more battery current than is needed during periods when the signal contains only one data stream. One possible solution would be to signal to the receiver the amount of required processing repeatedly during a connection, for example at every DTX event. However, a large amount of signalling would be required to do this, using valuable communication bandwidth.